<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <style>
    .watermarked::after {
      content: "Watermark";
      position: absolute;
      top: 50%;
      left: 50%;
      transform: translate(-50%, -50%);
      opacity: 0.5;
      font-size: 20px;
      color: gray;
    }
  </style>
</head>

<body>
  <div class="watermarked" style="position: relative; width: 300px; height: 200px; background-color: lightgray;">
    <p>这是一些内容。</p>
  </div>
</body>

</html>